The present invention relates to a spindle motor unit having a hydrodynamic bearing that can be used for a hard disk, and the like.
A conventional spindle motor unit having a hydrodynamic bearing is described below. FIG. 9 is a cross sectional view of a conventional spindle motor unit having a hydrodynamic bearing used for a hard disk, at rotation. FIG. 10 is an enlarged partial view of FIG. 9 illustrating a thrust bearing of the spindle motor unit at rest and placed in a normal position. FIG. 11 illustrates the thrust bearing shown in FIG. 10 at rest and placed in a vertically inverted position. FIG. 12 is a top view of flange 3 used in the spindle motor unit, and cross sectional views of flange 3 shown in FIGS. 10 and 11 are taken on lines 10(11)xe2x80x9410(11) of FIG. 12.
Referring to FIGS. 9 through 12, base 1 has radial bearing 1a and thrust support 1b. Rotating shaft 2 that co-axially rotates with respect to base 1 is supported by the radial bearing 1a. Flange 3 is secured to the lower end of rotating shaft 2 by a machine screw.
Flange 3 has grooves 3a and 3b formed of projections and depressions on its top and bottom faces, respectively. Plate 4 has thrust support 4a in a position opposed to grooves 3b on flange 3, and is secured to a bottom face of base 1 by a machine screw. Lubricant 5 exists between radial bearing 1a and rotating shaft 2, between thrust support 1b on base 1 and grooves 3a on flange 3, and between grooves 3b on flange 3 and thrust support 4a on plate 4. Hub 6 with magnetic disks 7 mounted thereon is co-axially fixed to rotating shaft 2.
In a spindle motor unit having a hydrodynamic bearing structured as above, a rotating body including magnetic disks 7 and rotating shaft 2 floats up in a predetermined position during its rotation; thereby such information as picture, audio, and text, is recorded into magnetic disks 7 or recorded information is reproduced from magnetic disks 7 through a magnetic head (not shown).
However, while the flange is at rest as shown in FIG. 10, circumferential projection 3d on the periphery of the bottom face of flange 3 and thrust support 4a on plate 4 are in intimate contact with each other. Therefore, immediately after start-up of rotating shaft 2, only a small amount of lubricant 5 exiting outside of the bearing can move into between grooves 3b and thrust support 4a. This phenomenon has caused the following problems: the rotating body including rotating shaft 2 does not float up in the predetermined position, the reliability of the bearing cannot be maintained, and a magnetic head (not shown) cannot correctly be positioned with respect to the magnetic disks to perform correct recording and reproduction of signals.
Similarly, when the motor is used in a vertically inverted position as shown in FIG. 11, circumferential projection 3c on the periphery of the top face of flange 3 and thrust support 1b on base 1 are in intimate contact with each other while the flange is at rest. Therefore, when rotating shaft 2 starts to rotate, lubricant 5 existing outside of the bearing cannot move into between grooves 3a and thrust support 1b easily. This phenomenon has also caused the following problems: the rotating body including rotating shaft 2 does not float up in the predetermined position, the reliability of the bearing cannot be maintained, and the magnetic head (not shown) cannot perform correct recording or reproducing to or from the magnetic disks 7.
The present invention addresses the problems of conventional spindle motor units discussed above. Therefore, it is an object of the present invention to provide a spindle motor unit having a hydrodynamic bearing that allows lubricant to easily move from the outside into the inside of the bearing at start-up of rotation to thereby ensure the reliability as a thrust bearing and correct recording and reproducing operations.
A spindle motor unit having a hydrodynamic bearing in accordance with a first exemplary embodiment of the present invention has an escape formed at a corner of the base facing to the periphery of the top face of the flange and a circumferential recess formed in the plate in a position facing to the periphery of the bottom face of the flange as shown in FIG. 2. At start-up of rotation, lubricant existing around the peripheries of the flange easily moves through the above escape in the base and the circumferential recess in the plate into the thrust bearing, thus floating up the rotating body in a predetermined position. Assuming the diameter of the escape in the thrust support on the base is xcfx86d1, the outermost diameter of the grooves on the top face of the flange is xcfx86d2, the outermost diameter of the grooves on the bottom face of the flange is xcfx86d3, the outer diameter of the flange is xcfx86d4, the outer diameter of the circumferential recess in the plate is xcfx86d5, the inner diameter of the circumferential recess is xcfx86d6, relations xcfx86d1 less than xcfx86d2, xcfx86d6 less than xcfx86d3, and xcfx86d4 less than xcfx86d5 hold.
In a spindle motor unit having a hydrodynamic bearing in accordance with a second exemplary embodiment of the present invention, areas around the peripheries of the top and bottom faces of the flange are formed with depressions as shown in FIG. 6. Since these depressions are continuous with the grooves on the top and bottom faces of the flange, lubricant existing around the peripheries of the flange moves into the thrust bearing easily at start-up of rotation, thus floating up the rotating body in the predetermined position.